It wasn't a piston. The intake on the bike blows up, and it is debris from that that hits him. I've seen many threads about this.
Oh, and before anyone starts, that isn't his hand that gets blown off, just the glove. The guy still races to this day (wears a ballistic vest now) and in fact, he won the national championship on that very same bike.
Due to the recent increase in spam in this forum, I've set it to New thread Moderation.
This simply means any new threads created here have to be aproved by a moderator or admin.
Sorry for any inconvenience this might cause.